One parameter in providing good performance and capacity for a given communications protocol in a communications network is packet data latency. Latency measurements can be performed in all stages of the communications network, for example when verifying a new software release or system component, and/or when deploying the communications network and when the communications network is in commercial operation.
Shorter latency than previous generations of 3GPP radio access technologies was one performance metric that guided the design of Long Term Evolution (LTE), corresponding to 3GPP Release 8 or higher. End user now recognize LTE as a system that provides faster access to the Internet and lower packet latency than previous generations.
Packet latency is also a parameter that indirectly influences the throughput of the communications network. Traffic using the Hypertext Transfer Protocol (HTTP) and/or the Transmission Control Protocol (TCP) is currently one of the dominating application and transport layer protocol suite used on the Internet. The typical size of HTTP based transactions over the Internet is in the range of a few tens of kilobytes up to 1 megabyte. In this size range, the slow start period of the TCP represents a significant part of the total transport period of the packet stream. During the TCP start period, the performance is packet latency limited. Hence, improved packet latency can potentially improve the average throughput, at least for this type of TCP-based data transactions.
Radio resource efficiency could also be positively impacted by packet latency reductions. Lower packet data latency could increase the number of transmissions possible within a certain delay bound; hence higher Block Error Rate (BLER) targets could be used for the data transmissions freeing up radio resources potentially improving the capacity of the system.
The existing physical layer downlink control channels, Physical Downlink Control Channel (PDCCH) and enhanced PDCCH (ePDCCH), are used to carry Downlink Control Information (DCI) such as scheduling decisions for uplink (UL; from device to network) and downlink (DL; from network to device) and power control commands. Both PDCCH and ePDCCH are according to present communications networks transmitted once per 1 ms subframe.
3GPP TS 36.212 lists examples of different DCI formats for UL and DL resource assignments. UL scheduling grants use either DCI format 0 or DCI format 4. The latter was added in the 3GPP for supporting uplink spatial multiplexing
The existing way of operation, e.g. frame structure and control signalling, are designed for data allocations in subframes of a fixed length of 1 ms, which may vary only in allocated bandwidth. Specifically, the current DCIs define resource allocations within the entire subframe, and are only transmitted once per subframe. The existing way of operation does not indicate how scheduling of UL and DL data can be performed in a shorter time frame than a subframe, i.e., shorter than 1 ms.
Hence, there is a need to reduce signalling overhead and implementation complexity.